This is spawned from the "Internal Vs External" thread. I feel it would be more productive to take a simple, basic task and discuss how that same task is accomplished by someone with an internal focus vs. someone with a traditional, athletic, external focus.

Setup: The receiver stands with their feet roughly shoulder width apart, arm raised to the side and extended, palm facing out. Their goal is to receive/resist a push to the palm of that hand while maintaining their upright structural integrity.

External method: The typical way that everyone I've ever experienced, including myself, responds to this is by tensing the muscles of the arm and shoulder first. For a low force push, this is usually enough to resist it and remain stable and upright, but as the force of the push increases, so does the amount of muscle tension that's introduced to hold the frame together and keep it rigid. Once fatigue sets in or the amount of force surpasses what the persons muscles can handle, the integrity of the frame starts to break down and they will be bent, pushed over, or often times will start leaning into the push to counter the force acting against their frame, making them susceptible to being off balanced by removing that force. Someone with more muscle (aka, strength) can resist more force for longer periods of time before that frame breaks down.

Internal Method: On the surface and at its most basic level, the goal is to maintain the structure of the frame. Where the two methods differ is that normally a person will flex muscle to hold the frame rigid against a force. Someone with an internal focus will instead relax those muscles, which in essence allows the joints of the body to compress upon themselves to maintain the structure of the frame. There is a significant amount of conditioning that goes into allowing this happen, so initially you can't do this against a high level of force. The muscles of the body will instinctively kick in to hold the frame, but with consistent, low force repetition the joints of the body and those 'inner muscles" become conditioned to support those forces without the major muscles of the body kicking in to support the frame. Initially you might find that while you're able to keep the shoulder relaxed against a light force, you'll notice that other muscles, your lower back muscles for instance, are firing up to hold the frame. In my experience, there is a progression of relaxing the muscles, conditioning the joints and then noticing where the muscular tension has moved and then focusing on relaxing/conditioning those areas. The end result, regardless of the amount force one can handle, is that the solidity of the ground is presented through the person's body. So that when a force acts against that body, it is in effect pushing on the ground. This is the earth in heaven and earth. It also has a side-effect of naturally keeping a persons weight down.

Int Notes 1: This is meant to be a very basic view of this particular aspect of IP. At progressing levels, there are other things that come into play to augment those conditioned joints, provide additional structure to assist in handling/distributing those forces and to further remove slack from the body so that there is no movement or slippage in the body and those forces are cleanly conveyed to the ground. The tensing of muscle breaks that conveyance of force. Intent also plays a big part in both using those other structures and also manipulating and routing those forces through the body to the ground and elsewhere. Also, the point I made about the joints compressing in on themselves is meant to be the most basic of basic. With some conditioning the joints stop behaving that way and again, intent plays a big part.

Int Note 2: While this may seem to be just another trick or technique, which on some level it may be, it is meant to be a system for how one carries their body, a state of being. You always carry your body this way and focus on keeping it that way, so that anything that comes in contact with your body is essentially coming in contact with the ground without the need to ready yourself or react. It's "just there" in the same way that a steel pole buried in the ground is always "just there" waiting for you to hit it and bounce off it. The steel pole doesn't have to become ready. It is always conveying the solidity of the ground back at anything that acts against it.

I believe that the distinction between these two modes of body usage to accomplish the same task are pretty clear. Feel free to comment and compare, but please, keep the comments focused on the basics of what this example is meant to cover.